The purpose of this project is to analyze the molecular events which result in a change in ion permability of the postsynaptic excitable membrane in response to neurotransmitter substances during synaptic transmission. The system studied in the inhibitory neuromuscular junction in arthropods and inhibitory synapses in mammalian central nervous systems including human where the neutrotransmitter compound is gamma-aminobutyric acid (GABA). The approach is to define, isolate, and study the membrane proteins involved in the phenoema; the receptor and ionophore proteins. The activity of these proteins is defined in vitro by radioactive ligand binding assays; the binding must be consistent with in vivo properties of the system. Radioactive GABA, picrotoxinin, and analogues are employed; the binding sites are being extensively characterized. Chemical studies on GABA agonist and antigonist compounds, and also convulsant and anti-convulsant drugs are part of this approach. Insights into the mode of action of several drugs (molecular pharmacology) will likely be obtained. Fractionation of tissue containing GABA receptors will allow enrichment of excitable membranes, which will be assayed in vitro for GABA regulation of ion permeability. With an unambiguous assay for the GABA receptor and perhaps ionophoer, these proteins will be localized to a cellular fraction, solubilized by mild detergents, their physical properties studied, and purified by affinity chromatography. The purified proteins will then be reconstituted into membranes for analysis of their molecular roles in the regulation of excitable membrane ion permeability by neurotransmitter substances. It is hoped that the complex cellular events of the synapse can be reduced to a biochemistry project. The purified proteins may be localized in brain by immunohistochemistry, and the protein turnover analyzed with respect to synaptogenesis and plasticity. The information gained will be related to biomedical problems of nerve and muscle tissues, including epilipsy and Huntington's Chorea.